1. Field of the Invention
The present invention relates generally to the field of vehicular wheelchair lifts which enable persons who are physically challenged or otherwise have limited mobility to board and leave a vehicle. More particularly, the present invention relates to the field of providing correction to the positioning movement of a platform of the wheelchair lift.
2. Description of the Prior Art
Vehicle lifts are widely used for enabling persons who are physically challenged or otherwise have limited mobility to board and leave vehicles. In using the wheelchair lift, it is important that the platform of the lift is accurately positioned.
One of the common arrangements of a vehicular wheelchair lift is shown in FIG. 1. Referring to FIG. 1, there is illustrated a vehicle 2, such as a bus, with a powered vehicular wheelchair lift 10 mounted underneath one of the access doors of the bus 2. The platform 12 of the lift 10 is illustrated in one of its various operating positions, which typically include a ground level position "G", a stow level position "S", and a floor level position "F" (the floor and ground level positions are designated in dashed lines as shown).
In control the movement of the platform 12, it is critical that the platform 12 can be positioned accurately at a "target" level. For example, if the platform needs to be at the stow level "S", then the target level is the stow level "S" and as the platform 12 moves toward the stow level "S" either from the ground level "G" below or from the floor level "F" above, the control mechanisms of the lift 10 should stop the platform 12 at the stow level "S". The movement of the platform 12 toward the stow level "S" is a positioning movement of the platform 12, which should end when the platform 12 arrives at the stow level "S".
However, since the positioning movement of the platform 12 is powered by the hydraulic, electric or other types of power mechanisms of the lift 10 and controlled by the positioning mechanisms of the lift 10, in real practice there is often an error between the target level and the actual level of the platform 12. This error will vary in a predicable manner by environment changes and mechanical wear. In the example shown in FIG. 1, the target level is the stow level "S", which is the level the platform 12 shoots for, but the platform does not come to a full stop at level "S". Rather, the actual position of the platform 12 is at level "P". The distance ".DELTA." between the target level "S" and the actual level "P" is the error of the positioning movement of platform 12. If the error is corrected in the same cycle in which it occurs, the cycle will be necessary increases. This is an undesirable side effect of a non-learning error correction system.
It is desirable to have a method of and apparatus for providing correction to the error in the positioning movement of the platform of a wheelchair lift. It is also desirable to have such a system respond to the variance of the error, due to the environment and/or mechanical changes. It is also desirable to provide for error correction while keeping cycle time at a minimum.